P130: Development of Nonquinone Hsp90 inhibitors by Biosynthetic Engineering

A biosynthetic engineering technique was applied to optimize the pharmacological properties of the benzoquinone ansamycin, geldanamycin. Geldanamycin and its natural or semi-synthetic derivatives have the potential to serve as anticancer chemotherapeutic agents. However, these first-generation Hsp90 inhibitors share an unfavorable benzoquinone structural feature that is manifested as a weakness in terms of its hepatotoxicity and resistance during clinical evaluation. The dose-limiting toxicity of geldanamycin and its derivatives may be partly “off target”, and could be attributable to the high chemical reactivity of its benzoquinone group and may not be a direct consequence of Hsp90 inhibition. For these reasons, a second generation of geldanamycin derivatives that lack a quinone moiety was proposed as alternative compounds to reduce undesirable toxic effects.We report the rationally designed biosynthesis of C15 hydroxylated non-quinone geldanamycin analogs by site-directed mutagenesis of the geldanamycin polyketide synthase (PKS), together with a combination of post-PKS tailoring genes. A 15-hydroxyl-17-demethoxy non-quinone analog, DHQ3, exhibited stronger inhibition of Hsp90 ATPase activity (4.6-fold) than geldanamycin. Taken together, the results of the present study indicate that rational biosynthetic engineering allows for the generation of derivatives of geldanamycin with superior pharmacological properties. [This work was supported in part by the 21C Frontier Microbial Genomics and Application Center]